Carbonyl reaction with amino acid

In order to improve this reaction, a proper understanding of all parameters affecting product yield is desired. Clearly, the high enzyme consumption is a major obstacle for an efficient and economically feasible process. A likely cause of the inefficient use of DERA in this conversion is enzyme deactivation resulting from a reaction of the substrates and (by-) products with the enzyme. In general, aldehydes and (z-halo carbonyls tend to denature enzymes because of irreversible reactions with amino acid residues, especially lysine residues. From the three-dimensional structure it is known that DERA contains several solvent-accessible lysine residues [25]. Moreover, the complicated reaction profile as shown in Scheme 6.5 indicates the potential pitfalls of this reaction. 

Upon reaction with amino acids, in the Strecker degradation, unstable imines are formed, which may easily decarboxylate, leaving an enamine, which upon hydrolysis yields an aldehyde from the amino acid and an a-aminoketone from the di-carbonyl-compound. 

In conclusion, this new organocatalytic direct asymmetric Mannich reaction is an efficient means of obtaining optically active //-amino carbonyl compounds. It is worthy of note that besides the enantioselective process, enantio- and diastereose-lective Mannich reactions can also be performed, which makes synthesis of products bearing one or two stereogenic centers possible. Depending on the type of acceptor or donor, a broad range of products with a completely different substitution pattern can be obtained. The range of these Mannich products comprises classic / -amino ketones and esters as well as carbonyl-functionalized a-amino acids, and -after reduction-y-amino alcohols. 

Oxidation modifications such as carbonylation, thiol oxidation, and aromatic hydroxylation, and Maillard glycation (the reaction of sugars with amino acid side chains) are the protein modifications most frequently reported in foodstuffs that have been subjected to thermal processing. However, condensations and eliminations of side chains or peptide backbone breakdown have also been described (95). 

M. Namiki, T. Hayashi, and S. Kawakishi, Free radicals developed in the amino-carbonyl reaction of sugars with amino acids, Agric. Biol. Chem., 1973, 37, 2935-2936. 

M. Namiki and T. Hayashi, Development of novel free radicals during amino-carbonyl reaction of sugars with amino acids, J. Agric. Food Chem., 1975, 23, 487 -91. 

In this reaction the H and OH highlighted in bold have been removed to form a molecule of water. The carbonyl of the amino acid on the left formed a bond with the nitrogen atom in the amino acid on the right. The amide functional group was formed in this dehydration synthesis reaction. Notice the ends of the newly formed dipeptide. There exists another amine group and carboxylic acid group at the ends of this chain to join with other amino acids and lengthen the chain. 

The PS-benzyloxycarbonyl resin (Fig. 16.2) shows at 1774 cm-1 the typical carbonyl absorption which disappears by loading the resin with amino acid fluorenylmethyl esters. This can be detected by a new carbonyl absorption at 1726 cm-1 and the characteristic C—C absorption band of the fluorene at 740 cm - which disappears by treating the resin with piperidine. The successful reaction to the Pfp-ester can be detected by the additional carbonyl absorption band at 1794 cm -1. The following reduction step to the amino alcohol is proofed by the disappearance of this band. The oxidation to the aldehyde and the formation of the imine is shown by the characteristic absorptions of new functional groups. [v(C—H, aldehyde = 2720 cm-1), imine (v(C=N) = 1670 cm-1].The successful Pictet-Spengler cyclization is proofed by the disappearance of the imine band. 

The reagent is prepared1 by the reaction of carbonyl chlorofluoride2 with /-butanol. Like f-butyl azidoformate, the reagent reacts with amino acids to give t-butyloxy-carbonylamino acids (BOC-amino acids).1... 

---